Hello, I'm the author of this article, and just wanted to add something here: for anyone who finds the Bullet Journal method overwhelming, there's another system called Strikethru that might appeal more. It's still based on pen and paper, but is designed to be a bit less complex and doesn't use an index at all.
And here are a couple of blog posts I've written about my own process that might be useful. I generally use a mixture of ideas from Bullet Journal and Strikethru.